The present invention is directed to an intraarterial prosthesis, a modular stent-graft, for repair of abdominal aortic aneurysm (xe2x80x9cAAAxe2x80x9d herein). Moreover, the present invention relates to a graft which embodies a reduced profile in its compressed condition as well as to facilitating the insertion, in vivo, of one element of a modular graft into another.
An intraarterial prosthesis for the repair of AAAs (grafts) is introduced into the AAA through the distal arterial tree in catheter-based delivery systems, and is attached to the non-dilated arteries proximal and distal to the AAA by an expandable framework (stents). An intraarterial prosthesis of this type has two components: a flexible conduit, the graft, and the expandable framework, the stent (or stents). Such intraarterial prosthesis used to repair AAAs is named stent-graft. AAAs typically extend to the aortic bifurcation of the common iliac arteries. There is rarely any non-dilated aorta below the aneurysm. If there is not then the distal end of the graft must be implanted in the lilac arteries, and for the graft to maintain prograde in-line flow to the legs and arteries of the pelvis, it must also bifurcate. Currently available stent-grafts fall into several categories. One category of grafts are those in which a preformed graft (either tube, aorto-mono-iliac or bifurcated) is inserted whole into the arterial system and manipulated into position about the AAA. This is a unibody graft. Another category of stent-grafts are those in which a graft is assembled in situ from two or more stent-graft components. This latter stent-graft is referred to as a modular stent-graft.
The use of modular stent-grafts may be attended by a number of problems. Generally, modular stent-grafts must be compressed for insertion and delivery into the vascular system in a delivery capsule. It will be appreciated that the larger the outer profile of the graft in its compressed condition, the more difficult it will be to insert the device into vasculature and to negotiate the twists and turns of the vasculature. Another significant problem is that, because of the restricted geometry of the vasculature, it can be difficult to insert one element of a modular stent-graft into another. Yet a further problem is that the aorta proximate the renal arteries can lack adequate healthy tissue for forming an attachment of the graft to the aortic wall.
Accordingly, there exists a need to provide a modular graft that can assume a profile better suited for navigating tortuous vasculature, and that is configured to facilitate assembly of its subcomponents. There is a further need to provide an apparatus which can be used where there is insufficient healthy aortic tissue near the renal arteries and which permits a fixation device thereof to be axially rotated with respect to the graft. The device of the present invention addresses these and other needs.
Briefly, and in general terms, the present invention is directed to a modular stent-graft comprising multi-components. The modular stent-graft of the present invention eliminates or avoids the main drawbacks common to the currently available modular stent-grafts for repair of AAAs. Stent-grafts are inserted into the AAA through the femoral arterial system. The graft must bridge the AAA and form a leak-proof conduit between the aorta and the iliac arteries. The surgeon can only view the operation by X-ray techniques and yet the surgery is performed in a three-dimensional environment. This is a demanding regime and requires a trained and skilled surgeon.
The main drawbacks common to the current modular stent-grafts are:
1. The connection site between the stent-graft components is prone to leakage and a separation of the components which allows blood to leak directly into the AAA restoring the potential for rupture. If the AAA ruptures, the result is frequently the death of the patient.
2. The connection site on the first stent-graft component is often difficult to catheterize prior to introduction of the second stent-graft component. The necessary instrumentation required to insert catheters and carry out the repair of the abdominal aneurysm can dislodge mural thrombus in the AAA. The dislodged mural thrombus is carried in the blood flow through the femoral arteries to small distal arteries causing blockage and tissue necrosis.
3. Modular stent-grafts are conventionally prepared for delivery with one or more stents positioned within a lumen of the graft, thus substantially adding to the profile of the stent-graft assembly. Moreover, additional stents positioned in separate branches of a bifurcated graft are conventionally located at the same axial level, thus adding to the profile of the graft. Further, due to the nature of modular stent-grafts, it is sometimes difficult to assemble, in vivo, the various components of conventional stent-grafts. These factors add to the difficulty of inserting and delivering a graft within the vasculature of a patient.
The modular stent-graft of the present invention consists of at least three stent-graft components. The first stent-graft component resembles a pair of shorts with the trunk proximal and the two legs or docking sites distal. The second and third stent-graft components are tubes of almost uniform diameter that extend from the primary stent-graft component docking sites, through the AAA, to the iliac arteries. The completed modular stent graft bridges the AAA from the abdominal aorta to the iliac arteries. The proximal ends of the second and third stent-graft components, i.e., ends nearest the aorta, are inserted into the docking sites of the primary stent-graft. The second stent-graft component is inserted through the ipsilateral arteries to the ipsilateral docking site of the primary stent-graft component. The second stent-graft is also referred to as the ipsilateral extension. The third stent-graft component is inserted through the contralateral arteries to the contralateral docking site through the bell-bottom portion of the primary stent-graft component. The third stent-graft is also referred to as the contralateral extension. Further extensions can be added to any of the stent-graft components to lengthen the overall system.
The modular stent-graft of the present invention has a number of distinguishing elements. The stents that hold the two docking sites open are at different levels and are of different sizes. On the ipsilateral docking site, the stent is within the docking site. With regard to the contralateral docking site, the stent is within a wider distal segment, the bell-bottom segment below the contralateral docking site.
Because the distal stents of the primary stent-graft component are at different levels, one below the other, they occupy different segments of the delivery system. Since the stent-graft components are delivered to the AAA through a narrow catheter, they must be reduced to the smallest possible diameter to effect and ease delivery. By separating the stent-graft into three components, the necessary stents can be arranged at different levels permitting them to be as large as possible. Since the distal stents can be larger in a modular system than in a unitary system, the distal orifice of the ipsilateral and contralateral docking site can be large and thus easier to catheterize for the delivery. This is only important on the contralateral side, that is, the side with the contralateral docking site. On the ipsilateral side, that is, the side with the ipsilateral docking site, catheters can be introduced over the same guide wire that was used to introduce the first stent-graft component through the arterial system to the AAA. In practice, the distal orifice of the contralateral docking site can be at least as large as the trunk of the primary stent-graft component. The first stent-graft component and the second and third stent-graft components and can be made of the same different biologically inert graft and stent material, such as biologically inert knit or woven fabric, or membrane material, such as PTFE membrane material, and springy material, such as stainless steel or titanium.
In a further aspect of the present invention, an expandable framework configured to attach a primary stent-graft component to vasculature is axially separated from the graft, the same being connected to the graft by flexible longitudinally extending members, or ties. Where the graft and expandable framework are thus separated, additional expandable frameworks may be added to the graft after deployment of the graft to perform the function of sealing the graft to vascular wall and/or to maintain the patency of the graft.
An advantage of providing a fixation device axially separated from the graft, and providing support structures after deployment of the graft within vasculature, is that the unassembled components of the graft assembly can assume a smaller profile for insertion into vasculature than would a fully assembled stent-graft. This improvement is further enhanced by placing at different levels, stents adapted to maintain the patency of the graft.
In one aspect of the invention, the flexible longitudinally extending members may be of such a length that an end of the graft abuts the fixation device. Alternatively, the flexible longitudinally extending members may be of sufficient length to provide a gap between the fixation device and the graft. In both embodiments, the fixation device can assume a different diameter than the graft and an axis of the graft can be at an angle with respect to an axis of the fixation device. By permitting this axial angulation, the graft device can be placed in angulated necks and an effective seal with the vascular wall can be better achieved.